Exploratory model analysis of the Space Based Infrared System (SBIRS) Low Global Scheduler problem

Transcription

1 Calhoun: The NPS Institutional Archive Theses and Dissertations Thesis Collection Exploratory model analysis of the Space Based Infrared System (SBIRS) Low Global Scheduler problem Morgan, Brian L. Monterey, California. Naval Postgraduate School

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6 NAVAL POSTGRADUATE SCHOOL Monterey, California THESIS EXPLORATORY MODEL ANALYSIS OF THE SPACE BASED INFRARED SYSTEM (SBIRS) LOW GLOBAL SCHEDULER PROBLEM by Brian L. Morgan December 1999 Thesis Advisor: Second Readers: Thomas W. Lucas Robert R. Read Thomas D. Gottschalk Approved for public release; distribution is unlimited.

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8 REPORT DOCUMENTATION PAGE Form Approved OMBNo Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA , and to the Office of Management and Budget, Paperwork Reduction Project ( ) Washington DC AGENCY USE ONLY (Leave blank) 2. REPORT DATE December REPORT TYPE AND DATES COVERED Master's Thesis 4. TITLE AND SUBTITLE EXPLORATORY MODEL ANALYSIS OF THE SPACE BASED INFRARED SYSTEM (SBIRS) LOW GLOBAL SCHEDULER PROBLEM 6. AUTHOR(S) Morgan, Brian L. 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Naval Postgraduate School Monterey, CA FUNDING NUMBERS 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING / MONITORING AGENCY REPORT NUMBER 11. SUPPLEMENTARY NOTES The views expressed in this thesis are those of the author and do not reflect the official policy or position of the Department of Defense or the U.S. Government. 12a. DISTRIBUTION / AVAILABILITY STATEMENT Approved for public release; distribution is unlimited. 13. ABSTRACT 12b. DISTRIBUTION CODE Proliferation of theater ballistic missile technologies to potential U.S. adversaries necessitates that the U.S. employ a defensive system to counter this threat. The system that is being developed is called the Space-Based Infrared System (SBIRS) "System of Systems." The SBIRS Low component of the SBIRS "System of Systems" will track strategic and theater ballistic missiles from launch to reentry and relay necessary cueing data to missile interceptors before the missiles reach friendly forces or countries whose safety is a vital interest to the U.S. SBIRS Low has a number of critical system requirements that for any given satellite are mutually exclusive for the length of time needed to complete the specified tasking. This limitation implies a system capacity on the total number of ballistic objects the SBIRS Low system can track at any given time. Applying exploratory model analysis, the SBIRS Low model uses the Monte Carlo method to explore large regions of the model space to identify key factors in the system and to provide insight into different tasking schemes for individual satellites. The exploratory model analysis, which consisted of 1 3,760,000 missiles being tracked in the analysis of the CSS-2 and M-9 missiles, yielded the following significant results: (a) defining the "best" satellite is nontrivial, (b) the SBIRS Low system was unable to initiate a booster track for an unacceptably large percentage of M-9 missiles launched near the equator, (c) if the system anticipates a long delay in revisiting a track, a stereo view should be scheduled immediately prior to the start of the delay, (d) mono viewing alone does not provide the required track accuracy, (e) track accuracy is a function of missile classification, and (0 the instantaneous track accuracy versus sensor revisit rate does not fit any well-known probability distribution. 14. SUBJECT TERMS Ballistic Missile Defense, Exploratory Model Analysis, Space-Based Infrared Systems 15. NUMBER OF MGES PRICE CODE 17. SECURITY CLASSIFICATION OF REPORT Unclassified 18. SECURITY CLASSIFICATION OF THIS PAGE Unclassified 19. SECURITY CLASSIFI- CATION OF ABSTRACT Unclassified 20. LIMITATION OF ABSTRACT UL NSN Standard Form 298 (Rev. 2-89) Prescribed by ANSI Std

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10 DUDLEY KNOX LIBRARY NAVAL POSTGRADUATE SCHOOL Approved for public release; distribution is unlimited EXPLORATORY MODEL ANALYSIS OF THE SPACE BASED INFRARED SYSTEM (SBIRS) LOW GLOBAL SCHEDULER PROBLEM Brian L. Morgan Lieutenant Commander, United States Navy B.S., University of Virginia, 1989 Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN OPERATIONS RESEARCH from the NAVAL POSTGRADUATE SCHOOL December 1999

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12 DUDLEY KNOX LIBRARY NAVAL POSTGRADUATE SCHOOL abstract MONTEREY CA Proliferation of theater ballistic missile technologies to potential U.S. adversaries necessitates that the U.S. employ a defensive system to counter this threat. The system that is being developed is called the Space-Based Infrared System (SBIRS) "System of Systems." The SBIRS Low component of the SBIRS "System of Systems" will track strategic and theater ballistic missiles from launch to reentry and relay necessary cueing data to missile interceptors before the missiles reach friendly forces or countries whose safety is a vital interest to the U.S. SBIRS Low has a number of critical system requirements that for any given satellite are mutually exclusive for the length of time needed to complete the specified tasking. This limitation implies a system capacity on the total number of ballistic objects the SBIRS Low system can track at any given time. Applying exploratory model analysis, the SBIRS Low model uses the Monte Carlo method to explore large regions of the model space to identify key factors in the system and to provide insight into different tasking schemes for individual satellites. The exploratory model analysis of the CSS-2 and M-9 missiles, in which over 1 3 million simulated missiles were tracked, yielded the following results: (a) defining the "best" satellite is nontrivial, (b) the SBIRS Low system was unable to initiate a booster track for an unacceptably large percentage of M-9 missiles launched near the equator, (c) if the system anticipates a long delay in revisiting a track, a stereo view should be scheduled immediately prior to the start of the delay, (d) mono viewing alone does not provide the required track accuracy, (e) track accuracy is a function of missile classification, and (f) the instantaneous track accuracy versus sensor revisit rate does not fit any well-known probability distribution.

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14 TABLE OF CONTENTS I. INTRODUCTION 1 A. OVERVIEW 1 B. BACKGROUND 3 C. PURPOSE AND RATIONAL 5 D. ORGANIZATION OF THESIS 6 H. SBIRS "SYSTEM OF SYSTEMS" AND EXPLORATORY MODELING OVERVIEW 7 A. SBIRS HIGH OPERATIONS 7 B. SBIRS LOW OPERATIONS 8 C. GLOBAL SCHEDULER 9 D. SYSTEM INTEGRATION 13 E. EXPLORATORY MODEL ANALYSIS 15 ffl. SBIRS PROBLEM AND ANALYSIS GENERALITIES 19 A. OVERALL ARCHITECTURE 19 B. SBIRS LOW PROBLEM 22 C. UNMODELED ASSUMPTIONS AND ISSUES 25 D. TRACKING AND MONTE CARLO ASSUMPTIONS 29 E. SCOPE OF ANALYSIS 32 IV. SBIRS LOW MODEL AND ANALYSIS SPECIFICS 37 A. BASIC MONTE CARLO STRUCTURE 37 B. BOOST SPECIFICS 42 C. KEPLER SPECIFICS 42 D. SAMPLE POINTS AND PREDICT-AHEAD 48 E. ANALYSIS SAMPLE SPACE 50

15 V. RESULTS 53 A. MODEL INPUT PARAMETERS 53 B. OUTPUT REPORT 55 C. ANALYSIS OF CSS-2 MISSILE DATA Ballistic Track Initiation Failure Synchronous Viewing Mono Viewing 70 D. ANALYSIS OF M-9 MISSILE DATA Ballistic Track Initiation Failure Synchronous Viewing Mono Viewing 84 E. COMPARISON OF CSS-2 AND M-9 MISSILE DATA 88 VI. CONCLUSION 95 APPENDIX A: MONTE CARLO METHODOLOGY 99 APPENDIX B:SBIRS LOW MODEL INPUT AND OUTPUT FILES 103 A. SB IRS LOW MODEL INPUT FILE FORMAT 103 B. SBIRS LOW MODEL OUTPUT FTLE FORMAT 106 APPENDIX C: CSS-2 MISSILE DATA 109 A. BALLISTIC TRACK INITIATION FAILURE 109 B. SYNCHRONOUS STEREO VIEWING 109 C. MONO VIEWING 110 D. SEQUENTIAL MONO VIEWING 112 E. ASYNCHRONOUS VIEWING 114 F. DELAYED VIEWING 120 G. STAGGERED VIEWING 122 H. LATITUDE SHIFT 125 APPENDIX D: M-9 MISSILE DATA 127 A. BALLISTIC TRACK INITIATION FAILURE 127

16 B. SYNCHRONOUS STEREO VIEWING 127 C. MONO VIEWING 128 D. SEQUENTIAL MONO VIEWING 130 E. ASYNCHRONOUS VIEWING 132 F. DELAYED VIEWING 138 G. STAGGERED VIEWING 140 H. LATITUDE SHIFT 143 LIST OF REFERENCES 145 BIBLIOGRAPHY 147 INITIAL DISTRIBUTION LIST 149

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18 LIST OF FIGURES 1. Diagram of Global Scheduler Track File Architecture SBIRS "System of Systems" Architecture with Communication Nodes Ballistic Missile Launch Timeline Ballistic Missile Launch Timeline Orbital Elements Eccentric Anomaly Depiction of True Anomaly CSS-2: Percentage Ballistic Track Initiation Failure Probability Density Function for Chi-Squared Distribution CSS-2: Synchronous Detection Using Sensors 1 and CSS-2: Histogram of Containment Bound CSS-2: Histogram of Containment Bound, First Five Bins Not Plotted CSS-2: Synchronous Detection Using Sensors 1 and CSS-2: Synchronous Detection Using Sensors 2 and CSS-2: Mean Containment Bounds Using Synchronous Detection Satellite Line-of-Sight and Missile's Orbital Plane CSS-2: 95% Containment Bounds Using Synchronous Detection CSS-2: 99% Containment Bounds Using Synchronous Detection CSS-2: Mono Detection Using Sensor CSS-2: Mono Detection Using Sensor CSS-2: Mono Detection Using Sensor CSS-2: Mean Containment Bounds Using Mono Detection CSS-2: 95% Containment Bounds Using Mono Detection CSS-2: 99% Containment Bounds Using Mono Detection M-9: Percentage Ballistic Track Initiation Failure Probability Density Function for Chi-Squared Distribution M-9: Synchronous Detection Using Sensors 1 and M-9: Synchronous Detection Using Sensors 1 and M-9: Synchronous Detection Using Sensors 2 and M-9: Mean Containment Bounds Using Synchronous Detection M-9: 95% Containment Bounds Using Synchronous Detection M-9: 99% Containment Bounds Using Synchronous Detection M-9: Mono Detection Using Sensor M-9: Mono Detection Using Sensor M-9: Mono Detection Using Sensor M-9: Mean Containment Bounds Using Mono Detection M-9: 95% Containment Bounds Using Mono Detection M-9: 99% Containment Bounds Using Mono Detection CSS-2 & M-9: Mean Containment Bounds Using Synchronous Detection CSS-2 & M-9: Mean Containment Bounds Using Mono Detection CSS-2 & M-9: 95% Containment Bounds Using Synchronous Detection CSS-2 & M-9: 95% Containment Bounds Using Mono Detection CSS-2 & M-9: 99% Containment Bounds Using Synchronous Detection CSS-2 & M-9: 99% Containment Bounds Using Mono Detection 93

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20 LIST OF TABLES 1 Exploratory Regions CSS-2: Ballistic Track Initiation Failure CSS-2: Synchronous Detection Using Sensors 1 and CSS-2: Synchronous Detection Using Sensors 1 and CSS-2: Synchronous Detection Using Sensors 2 and CSS-2: Mono Detection Using Sensor 1 Ill 7. CSS-2: Mono Detection Using Sensor CSS-2: Mono Detection Using Sensor CSS-2 Sequential Mono Viewing: Sensor 1 Handover to Sensor 2 at Time t = 75 seconds CSS-2 Sequential Mono Viewing: Sensor 1 Handover to Sensor 2 at Time t = 150 seconds CSS-2 Sequential Mono Viewing: Sensor 1 Handover to Sensor 3 at Time t = 75 seconds CSS-2 Sequential Mono Viewing: Sensor 1 Handover to Sensor at Time t = 150 seconds CSS-2 Sequential Mono Viewing: Sensor 2 Handover to Sensor 3 at Time t = 75 seconds CSS-2 Sequential Mono Viewing: Sensor 2 Handover to Sensor 3 at Time t = 150 seconds CSS-2 Asynchronous Viewing: Sensor 1 andsensor CSS-2 Asynchronous Viewing: Sensor 1 and Sensor CSS-2 Asynchronous Viewing: Sensor 1 and Sensor CSS-2 Asynchronous Viewing: Sensor 1 andsensor CSS-2 Asynchronous Viewing: Sensor 1 and Sensor CSS-2 Asynchronous Viewing: Sensor 1 and Sensor CSS-2 Asynchronous Viewing: Sensor 2 and Sensor CSS-2 Asynchronous Viewing: Sensor 2 and Sensor CSS-2 Asynchronous Viewing: Sensor 2 and Sensor CSS-2 Asynchronous Viewing: Sensor 2 and Sensor CSS-2 Asynchronous Viewing: Sensor 2 and Sensor CSS-2 Asynchronous Viewing: Sensor 2 and Sensor CSS-2 Asynchronous Viewing: Sensor 3 and Sensor CSS-2 Asynchronous Viewing: Sensor 3 and Sensor CSS-2 Asynchronous Viewing: Sensor 3 and Sensor CSS-2 Asynchronous Viewing: Sensor 3 and Sensor CSS-2 Asynchronous Viewing: Sensor 3 and Sensor CSS-2 Asynchronous Viewing: Sensor 3 and Sensor CSS-2 Delayed Viewing: Sensor 1 andsensor CSS-2 Delayed Viewing: Sensor 1 and Sensor CSS-2 Delayed Viewing: Sensor 1 and Sensor CSS-2 Delayed Viewing: Sensor 1 and Sensor CSS-2 Delayed Viewing: Sensor 1 and Sensor CSS-2 Delayed Viewing: Sensor 1 and Sensor CSS-2 Staggered Viewing: Sensor 1 and Sensor CSS-2 Staggered Viewing: Sensor 1 and Sensor CSS-2 Staggered Viewing: Sensor 1 and Sensor CSS-2 Staggered Viewing: Sensor 1 and Sensor 2 124

21 43. CSS-2 Staggered Viewing: Sensor 1 and Sensor CSS-2 Staggered Viewing: Sensor 1 and Sensor CSS-2 Latitude Shift to N02: Sensor 1 and Sensor CSS-2 Latitude Shift to N20: Sensor 1 and Sensor CSS-2 Latitude Shift to N60: Sensor 1 and Sensor CSS-2 Latitude Shift to N80: Sensor 1 and Sensor M-9: Ballistic Track Initiation Failure M-9: Synchronous Detection Using Sensors 1 and M-9: Synchronous Detection Using Sensors 1 and M-9: Synchronous Detection Using Sensors 2 and M-9: Mono Detection Using Sensor M-9: Mono Detection Using Sensor M-9: Mono Detection Using Sensor M-9 Sequential Mono Viewing: Sensor 1 Handover to Sensor 2 at Time t = 75 seconds M-9 Sequential Mono Viewing: Sensor 1 Handover to Sensor 2 at Time t = 150 seconds M-9 Sequential Mono Viewing: Sensor 1 Handover to Sensor 3 at Time t = 75 seconds M-9 Sequential Mono Viewing: Sensor 1 Handover to Sensor 3 at Time t = 150 seconds M-9 Sequential Mono Viewing: Sensor 2 Handover to Sensor 3 at Time t = 75 seconds M-9 Sequential Mono Viewing: Sensor 2 Handover to Sensor 3 at Time t = 150 seconds M-9 Asynchronous Viewing: Sensor 1 and Sensor M-9 Asynchronous Viewing: Sensor 1 and Sensor M-9 Asynchronous Viewing: Sensor 1 and Sensor M-9 Asynchronous Viewing: Sensor 1 and Sensor M-9 Asynchronous Viewing: Sensor 1 and Sensor M-9 Asynchronous Viewing: Sensor 1 and Sensor M-9 Asynchronous Viewing: Sensor 2 and Sensor M-9 Asynchronous Viewing: Sensor 2 and Sensor M-9 Asynchronous Viewing: Sensor 2 and Sensor M-9 Asynchronous Viewing: Sensor 2 and Sensor M-9 Asynchronous Viewing: Sensor 2 and Sensor M-9 Asynchronous Viewing: Sensor 2 and Sensor M-9 Asynchronous Viewing: Sensor 3 and Sensor M-9 Asynchronous Viewing: Sensor 3 and Sensor M-9 Asynchronous Viewing: Sensor 3 and Sensor M-9 Asynchronous Viewing: Sensor 3 and Sensor M-9 Asynchronous Viewing: Sensor 3 and Sensor M-9 Asynchronous Viewing: Sensor 3 and Sensor M-9 Delayed Viewing: Sensor 1 and Sensor M-9 Delayed Viewing: Sensor 1 and Sensor M-9 Delayed Viewing: Sensor 1 and Sensor M-9 Delayed Viewing: Sensor 1 and Sensor M-9 Delayed Viewing: Sensor 1 and Sensor M-9 Delayed Viewing: Sensor 1 and Sensor M-9 Staggered Viewing: Sensor 1 and Sensor M-9 Staggered Viewing: Sensor 1 and Sensor 2 141

22 88. M-9 Staggered Viewing: Sensor 1 and Sensor M-9 Staggered Viewing: Sensor 1 and Sensor M-9 Staggered Viewing: Sensor 1 and Sensor M-9 Staggered Viewing: Sensor 1 and Sensor M-9 Latitude Shift to N02: Sensor 1 and Sensor M-9 Latitude Shift to N20: Sensor 1 andsensor M-9 Latitude Shift to N60: Sensor 1 and Sensor M-9 Latitude Shift to N80: Sensor 1 and Sensor 2 144

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24 GLOSSARY OF TERMS AND ACRONYMS Clutter: any tactically insignificant set of tracking objects, e.g., noise, solar radiation, etc. Detection: any received signal from an object whose value is above the threshold for a sensing system. Discrimination: to make a distinction between the lethal object and all other non-lethal objects. Divert maneuver: change in velocity of the interceptor needed for a collision to occur. If an interceptor does not have sufficient propulsive capability to accomplish the required maneuver, additional interceptor(s) must be allocated to the target to destroy it. Dwell time: length of time that a sensor stares at an object. Event: the occurrence of a ballistic missile launch. False alarm: one or more signals, without "interesting" origins, that exceed the detection threshold. A random false alarm may be caused by persistent and/or structured clutter. Generalized energy management maneuver (GEMM): a coning maneuver by an object taking place in the boost phase and is used to expend excess energy, complicate counter-targeting, and/or prevent tracking systems from reverse-tracking the missile to its launch point. Additionally, since the maneuver affects the range of the missile, it may be used when either a depressed or lofted launch is not feasible or desirable. In-flight target update (IFTU): a mid-course position update in estimated position of the object given to the interceptor. Kepler orbit: the non-powered, ballistic phase of a missile's trajectory. with the earth located at one focii and the only force acting on the object is gravity. The trajectory is elliptical Kinematic tracking: a procedure in which each sensor, using its own data, forms polynomial fits through a fixed number of detections (typically cubic fits through six detections). Lethal object: warhead associated with a ballistic missile. A ballistic missile may have more than one lethal object contained within it. Long wavelength infrared (LWTR): this band generally covers the wavelengths between 8-14 micrometers and is used by space based sensors to detect and track objects above the horizon against a cold space background. Maneuver in the field of view (ManFOV): a compound situation consisting of sufficient divert maneuver and the target image lying within the interceptor seeker's field of view. Both of these conditions must be achieved for a successful intercept to occur. Medium wavelength infrared (MWTR): this band generally covers the wavelengths between 3-8 micrometers and is used by space based sensors to detect and track objects through booster burnout against an Earth background (i.e., below the horizon against a warm background).

25 Missile classification: the variant of missile launched, i.e., SCUD, CSS-2, M-9, etc. Mono track: an object whose positional data is derived from one or more successive line-ofbearing detections from a single sensor. Non-lethal object: any object, except a warhead, which continues on a ballistic trajectory after booster burnout. Periapsis: the point nearest the prime focus. ballistic object reaches its highest altitude. In the context of this research, the point at which the Post-boost vehicle (PBV): nose-section of the missile that contains lethal and non-lethal objects. Precision track: track generalized by physics-based equations of motion (e.g., Kepler motion for ballistic objects). Resolution: smallest distance between two objects at which the system can distinguish two separate objects. Revisit rate: scan rate for a sensor to return to an object. Revisit scheme: sensor tasking strategy used to ensure all objects are tracked within a specified positional accuracy. Scissors angle: the smallest angle formed by the line of sight to an object from two sensors with the object at the vertex. Short wavelength infrared (SWTR): this band generally covers the wavelengths between 1-3 micrometers and is used by space based sensors to see the bright rocket plumes of boosting missiles. Slew-settle-stare: the process in which a sensor is directed from one object to another, allowed to dampen any induced vibrations, and then "looking at" the object. Stereo track: an object whose positional data is derived from successive intersecting line-ofbearing detections from two or more sensors. Three-dimensional (3D) mono track: a track developed from a single sensor over several time periods. It provides range, azimuth, and elevation. To develop a 3D mono track, an active sensor or assumption of a rigid wire model is required. Three-dimensional (3D) stereo track: a track developed from two or more line-of-sight sensors in which azimuth and elevation data is combined to derive range. Track: a set of position coordinates and associated information that are associated with a single origin or cause. It should be noted that a track has an underlying system model, a mathematical formalism to determine properties of the underlying object based on the observed detections. Two-dimensional (2D) mono track: a track developed from the initial conditions at booster burnout and a single line-of-sight sensor. The only trajectory data provided is azimuth and elevation.

26 Very long wavelength infrared (VLWIR): this band generally covers the wavelengths between micrometers and is used by space based sensors to track targets against a space background.

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28 EXECUTIVE SUMMARY Proliferation of theater ballistic missile technologies to potential U.S. adversaries necessitates that the U.S. employ a defensive system to counter this threat. The system that is being developed is called the Space-Based Infrared System (SBIRS) "System of Systems." The SBIRS Low component of the SBIRS "System of Systems" will track strategic and theater ballistic missiles from launch to reentry and relay necessary cueing data to missile interceptors before the missiles reach friendly forces or countries whose safety is a vital interest to the U.S. The Space-Based Infrared System (SBIRS) architecture is an evolutionary step forward in the United States' forty-year program of employing space-based infrared surveillance system. The "SBIRS System of Systems" is comprised of two separate satellite constellations, SBIRS High and SBIRS Low. SBIRS High is comprised of four satellites in geostationary earth orbit, two satellites in highly elliptical orbits, and ground assets. The first satellite launch is scheduled for The SBIRS Low will feature 25 to 30 satellites in low earth orbit (analysis in this report is done for a particular 27 satellite constellation) and will be fully operational in The SBIRS Low component will bring an entirely new capability to the warfighter the ability to track theater and intercontinental ballistic missiles from launch to reentry and to relay necessary cueing data to missile interceptors before the missiles reach friendly forces. The SBIRS Low system must orchestrate surveillance of the entire post-boost threat, in support of a number of system requirements such as: track maintenance, discrimination of lethal (i.e., warhead) and non-lethal objects, precise track estimates and updates for interceptors, interceptor-lethal object kill assessment, and battlefield characterizations. For any given satellite, these requirements are mutually exclusive for the length of time needed to complete the specified tasking. This limitation implies a system capacity on the total number of ballistic objects the SBIRS Low system can track. At early stages in the analysis of a new system, the emphasis is on developing a broad understanding of the critical elements in the system and its potential applications. In such situations, there may be too much uncertainty to reliably estimate optimal solutions with the available tools. The SBIRS program is at such a stage. The SBIRS Low model was used to explore large regions of model space in an attempt to identify key factors in the system and scenarios to provide insight into the global scheduler problem, i.e., tasking of individual satellites.

29 The primary goal of this project is to explore various sensor tasking strategies that could be used by the SBIRS Low system, as controlled by the global scheduler, and characterize their effectiveness under different operating conditions. The tasking problem for SBIRS Low is nontrivial for the following reasons: a. The underlying scenario can be very dynamic with feasible sensor-to-target pairings (determined by some given criterion) changing over time. b. The track sensor is a limited resource, implying restrictions on the system target handling capacity. c. SBIRS Low has a number of system requirements that are mutually incompatible from the perspective of tasking, which results in variable demands being placed on individual sensors. d. A large number of target-specific tasks place time-dependent constraints on sensor assets. An example of a time -dependent task is the length of time a sensor "stares" at a target in an attempt to detect it. Because there is so much uncertainty in the SBIRS "System of Systems," it is the ideal candidate for exploratory analysis. The exploratory modeling search strategy used in this analysis is based upon the notion that simple models must first be implemented and explored in some detail in order to gain the intuition needed for the actual system design. The probability of SBIRS mission success, where success is defined as destruction of the lethal object, is of the general form P(success) = P(acquire n track n discriminate n target n kill). With a probability of mission success that exceeds 0.99, if a track on a lethal object is lost or dropped, intercept becomes nearly impossible. Thus, there is a necessity for an in depth understanding of this complex architecture. A typical timeline of events for a missile launch is shown in Figure 1

30 Figure 1. Representative missile launch timeline. Mid-course range = 150 seconds Lethal object Intercept Range ~ 90 seconds The SBIRS Low model makes certain assumptions regarding orbital mechanics and missile detection criteria. These assumptions represent a balance between achieving a desired level of insight and the recognition that a model cannot include every contingency. Additionally, certain aspects that are critical to SBIRS Low performance are ignored because they are functionally irrelevant for this analysis. For example, the communication architecture, specific design parameters of the interceptor, and all logistic constraints associated with an interceptor battery provide no additional insight into tracking accuracy. The SBIRS Low modeling goals are to: (1) develop of a system analysis methodology, (2) identify/explore sensitivities, (3) develop intuition, and (4) provide benchmark/reference book of track accuracies as a function of missile type, sensor revisit scheme, length of time since booster burnout (i.e., length of time in free-flight), and length of predict-ahead time. The SBIRS Low model is a Monte Carlo computer simulation that uses "appropriate fidelity" code for actual system components and physics-based equations of motion. The chosen fidelity is a trade-off between computational speed and resources, complexity of formulas, inclusion of parameters, and desired level of insight.

31 The analysis consisted of examining the system tracking accuracy for two of the nine types of missiles available to the user. These missiles, the CSS-2 and M-9, were chosen because of their dynamic flight characteristics. The exploratory model analysis included over 688 simulation events and each event consisted of 20,000 individual missile launches. Two results from the analysis are presented: (a) the failure of the system to initiate a ballistic track on a M-9 missile launched near the equator and (b) track position accuracy for a given sensor tasking strategy. Figure 2 shows the fraction of ballistic track initiation failures as a function of ballistic track revisit rate for three different boost phase sensor revisit rates for the M-9 missile. In all three cases, an "unacceptably" large number of ballistic track initiation failures were encountered. The counts of track initiation failures for the M-9 missiles are well characterized by a Poisson distribution. M-9: Fraction of Ballistic Track Initiation Failures 5 second booster revisit rate 3 second booster revisit rate 2 second booster revisit rate revisit rate (sec) Figure 2. Line plots of the fraction of ballistic track initiation failures for a M-9 missile at eight different ballistic sensor revisit rates. Figure 3 is representative of the analysis of the data provided by the SBIRS Low model. It shows the estimation error for three empirical containment bounds for a CSS-2 missile at time t = 50 seconds (after booster burnout).

32 CSS-2: Synchronous Detection Using Sensors 1 & 2 mean containment bound 95% containment bound 99% containment bound revisit rate (sec) Figure 3. CSS-2: Synchronous Detection Using Sensors 1 and 2. Line plot of the revisit rate versus estimation error for a CSS-2 missile using a stereo symmetric tasking scheme for the closest and next closest satellite. The exploratory model analysis yielded the following significant results: (a) defining the "best" satellite (based on sensor-to-target range, viewing geometry criteria, etc.) is nontrivial, (b) the SBIRS Low system was unable to initiate a booster track for an unacceptably large percentage of M-9 missiles launched near the equator, (c) if the system anticipates a long delay in revisiting a track, a simultaneous detection by two different sensors should be scheduled immediately prior to the start of the delay, (d) repeated detections by a single sensor alone does not provide the required track accuracy, (e) track accuracy is a function of the type of missile launched, and (f) the instantaneous track accuracy versus sensor revisit rate does not fit any well-known probability function.

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34 I. INTRODUCTION A. OVERVIEW Throughout history, military leaders have sought to gain the high ground advantage, and by achieving this goal, commanders were able to survey large areas of the battlefield, watch enemy troop movements, and guard against surprise attacks. With the development of rocket engine technology and the atomic bomb, by the middle of the Cold War the military high ground moved to outer space. The Space-Based Infrared System (SBIRS) architecture is an evolutionary step forward in the United States' space-based infrared surveillance system. The United States' first spacebased infrared system was called Missile Defense Alarm System (MIDAS). This program was started in 1960 and the concept of using space-based infrared detectors and other technologies was proven by Additionally, in 1963, the Vela program was developed to monitor compliance with the nuclear test ban treaty. In 1970, these two programs were consolidated into the Defense Support Program (DSP), an early warning satellite system operated by Air Force Space Command (AFSPC) and developed by the Air Force's Space and Missile Systems Center. DSP provides twenty-four hour, worldwide surveillance for missile warning and nuclear burst detection and serves as the space segment of the U.S. Integrated Tactical Warning and Attack Assessment System. The DSP system consists of several satellites in geostationary orbit, an Overseas Ground Station (OGS) in Australia, a European Ground Station (EGS), a continental U.S. (CONUS) Ground Station (CGS), and Mobile Ground Terminals (MGTs). The infrared detector arrays on each satellite have the capability to view nearly an entire hemisphere of the earth and can detect hot plumes from boosting missiles from any location within its field of view. The data collected during these sweeps is relayed down to one of the three Air Force ground stations or MGTs around the world and then communicated to the National Command Authority or to commanders in the field. A follow-on program to DSP is currently under development. This program is called "SBIRS System of Systems" and is comprised of two separate satellite constellations, SBIRS High and SBIRS Low. The SBIRS system is designed to perform the following four functions:

35 a. Missile warning - Utilizing over 25 years of experience on DSP and state-of-the-art technology, missile warning capabilities will significantly increase, and space-based platforms will better provide missile warning information to commanders. b. Missile defense - This mission will be satisfied using space-based infrared platforms to track targets from initial boost phase through mid-course, and the tracking data will be relayed to interceptors. c. Technical intelligence - Using multiple platforms, space-based infrared sensors will provide valuable data necessary for missile characterization and phenomenology and collect information on various other military systems and operations. d. Battlespace characterization - Capitalizing on the advantages of space-based infrared sensors, commanders will be able to assess interceptor hit/failure and battle damage and track infrared-intense events to improve battlefield situational awareness. [Ref. 1] SBIRS High is scheduled for first launch in 2004 and will feature a mix of four satellites in geostationary earth orbit, two satellites in highly elliptical orbits, and ground assets. Ground assets include a CONUS based Mission Control Station (MCS), a backup MCS, a survivable MCS, overseas relay ground stations, relocatable terminals, and associated communications links. The primary objective of SBIRS High is to detect and track the boost phase of theater and intercontinental ballistic missiles and communicate trajectory parameters to the ground assets. The SBIRS Low component will bring an entirely new capability to the warfighter the ability to track theater and intercontinental ballistic missiles from launch to reentry and to relay necessary cueing data to missile interceptors before the missiles reach friendly forces. When fully operational in 2006, the SBIRS Low component will consist of 25 to 30 satellites in low earth orbit (analysis in this report is done for a particular 27 satellite constellation). Each SBIRS Low satellite has two infrared sensors with which to perform its missions. One sensor, known as the acquisition sensor, will be a wide field of view scanning infrared sensor that will watch for short-wave infrared electromagnetic energy associated with missile plumes during the boost phase. Once the acquisition sensor has located a boosting missile, it begins to compute a trajectory for initialization of the ballistic track. Upon booster burnout, the initialization data for the ballistic track is transferred to the second on-board sensor. This sensor, called the track sensor, is a narrow field of view, high-precision staring sensor that is capable of detecting electromagnetic energy in multiple infrared bands. Mounted on a two-axis gimbal, the track sensor is capable of detecting post-booster burnout objects which may or may not contain various numbers of lethal objects or warheads, attitude control modules, spent booster rockets,

36 and decoys or penetration aids. The track sensor will track all objects through their mid-course trajectory and into their reentry phase. By this time, the on-board processing is supposed to have discriminated the lethal object(s), predicted the final ballistic trajectory of all objects, and estimated the lethal object's impact point and time of impact. This data will then be relayed to interceptor batteries where it will be used to intercept the incoming warhead(s). [Ref. 2] Utilizing tracking data from SBIRS Low, the area defendable by a single interceptor battery increases dramatically. Whereas systems like the Patriot require that the missile be within view of its ground-based radar before it can fire, SBIRS Low will provide cueing information to interceptors while warheads are still far away from friendly forces. This additional targeting capability will allow earlier engagements and multiple interceptor attempts on incoming missiles to increase the likelihood of a successful kill. Additionally, the entire constellation will be networked together using inter-satellite crosslinks, thus allowing each satellite to communicate with all other satellites in the constellation. This capability allows for satellite-to-satellite "handover" of target tracks. Target handover is required because the dynamic nature of the orbiting satellites and uncertainty of the launch point and time makes it extremely unlikely any one satellite will track a missile during its entire flight duration. If necessary, this type of handover will continue between satellites in the constellation until the target has been destroyed, its infrared energy can no longer be detected, or the missile impacts the surface of the earth. Additionally, SBIRS High satellites are networked, via ground relay, with SBIRS Low satellites and, if tactically prudent, can provide cueing to multiple SBIRS Low track sensors in near real-time for an extremely limited number of tracks. B. BACKGROUND SBIRS Low will "bridge the gap" between initial launch detection, the current capability of DSP and SBIRS High, and ground-based radar interceptors. Its primary function is to provide precise mid-course tracking and discrimination of objects for the SBIRS missile defense mission in theater conflicts and attacks against North America. The SBIRS Low system must orchestrate surveillance of the entire post-boost threat, in support of a number of system requirements such as: a. Track maintenance on all relevant objects until the lethal object is destroyed, the missile is judged not to be a threat and the track is dropped, or the lethal object impacts the earth.

37 b. Discrimination of lethal and non-lethal objects. c. Precise track estimates and updates for interceptors. d. Interceptor-lethal object kill assessment. e. Battlefield characterizations. [Ref. 3] For any given satellite, these requirements are mutually exclusive for the length of time needed to complete the specified tasking. This limitation implies a system capacity on the total number of objects the SBIRS Low system can track in the ballistic phase. With SBIRS Low, tracking, per se, is not an issue because the track sensor is sensitive enough to detect and discriminate objects with sufficient accuracy given most sensor-to-object geometries. The most critical issues are at the system level and these issues are tasking in highly dynamic environments and accomplishing the multiple system level requirements listed in the previous paragraph. The component in the SBIRS Low system that is responsible for "partitioning" active entries from the track file, a listing of all objects being tracked, is called the global scheduler. The global scheduler receives tasking requirements internally, from an acquistion sensor which detects a boosting missile, or externally from sources such as a Mission Control Station. Based on the tasking requirements, the global scheduler directs the operation of track sensors via local schedulers on-board each satellite. When operating within designed capacity, the global scheduler will fulfill this tasking while maintaining the specified level of tracking accuracy for all objects. Levels of tracking accuracy include simple detection, continual object discrimination, and target quality. These criterion can be established at some given level of confidence at the time of detection and predicted ahead to provide an approximate time at which, without an update, tracking accuracy will degrade below the defined minimum acceptable level. When the tracking accuracy for at least one track drops below the currently defined minimum acceptable level, the entire SBIRS Low system is defined to be in an overload condition. The system decision-aid will then suggest operator action necessary to relieve the overload based on utility assigned to available options. Examples of suggested operator action include no longer performing the mission of space surveillance, "dropping track" on a non-lethal object, or dropping track on a group of objects (e.g., sacrificing Pittsburgh to save Cleveland).

38 C. PURPOSE AND RATIONALE The primary goal of this project is to explore feasible track revisit schemes available to the global scheduler and characterize their effectiveness under different operating conditions and conditions that result in an overload. Using exploratory model analysis, the model space can be systematically searched over a variety of assumptions and hypotheses to reveal how the system would behave if the various guesses were correct. This type of analysis produces useful results through the creation of alternative feasible model outcomes. A sensitivity analysis is subsumed in the exploratory model analysis process, which inherently provides insight into which parameters are critical by the fact that its results are not predicated on any single point. Computer simulation and modeling plays a vital role in achieving insights which will aid in the quantification of uncertainties and determining feasible track revisit schemes for given predict ahead track position error bounds. The SBIRS Low model will provide ballistic missile launches that will be detected and tracked by the SBIRS Low satellite system and Monte Carlo simulations will be used to explore tasking and contingency operations models, target handling capacities, and system failure modes. Examples of tasking operations are using only the closest and second closest sensor from the target to track the target, using only the closest and third closest sensor from the target to track the target, or using only the second and third closest sensor from the target to track the target. In a dense tracking or sensor-deficient scenario, only one sensor may be available to track a target. These operations will each produce slightly different system behavior because: a. As the range from the sensor to the target increases, target positional error increases due to uncertainty in the focal plane pointing angle. b. Randomly assigned sensor bias errors that are varied each launch event. c. Differences in available tracking data, i.e., two sensors providing positional data via intersecting lines of bearing versus positional data derived from single lines of bearing taken from one sensor over some given time interval. d. Different contingency operations, i.e., conducting the analysis for different types of ballistic missiles (nine different missiles are currently modeled). Based on the feasible track revisit schemes, the output can be used as input for follow-on analysis of system overload behavior.

39 Thus, through a high dimensional exploration of the model, this analysis will: a. Determine how often a track needs to be updated to remain within a prescribed positional uncertainty. b. Determine the distribution for positional uncertainty as a function of revisit time. c. Determine the tracking capacity of the system in a variety of scenarios. d. Determine the critical factors that result in an overload condition. D. ORGANIZATION OF THESIS Following this introduction, the report is divided into five additional chapters. First, the SBIRS "System of Systems" is described in additional detail. Building on this additional information, specific design and requirements of the global scheduler are examined. The final section of this chapter provides a general overview of exploratory model analysis and why this analysis is appropriate at the present stage of the SBIRS Low development. Next, the architecture of the SBIRS Low system is further refined to include engineering complications, a definition of SBIRS mission success, and a typical timeline for a ballistic missile launch scenario. The assumptions present in the SBIRS Low model and their impact are listed in chronological order, according to the launch scenario. The chapter ends with a discussion of tracking and Monte Carlo assumptions. Next, the specifics of the SBIRS Low model are explained. The Monte Carlo structure of the model is further detailed and a prediction on the distribution of the track accuracy is presented. An overview of orbital mechanics is presented to ensure that the reader has an understanding of the underlying astrodynamics applicable to the SBIRS Low model. The chapter concludes with a description of the analysis sample space. Finally, the results of the exploratory model analysis are presented. The results are followed by a conclusion, which includes suggestions for additional research.

40 SBIRS "SYSTEM OF SYSTEMS" AND EXPLORATORY MODELING OVERVIEW A. SBIRS HIGH OPERATIONS The SBIRS "System of Systems" will provide the enhanced capabilities necessary to combat evolving theater and ballistic missile threats and help meet U.S. infrared space surveillance needs through the next several decades. The system will integrate space assets in multiple orbit configurations with a consolidated ground segment to provide more effective integration of data, improved tracking accuracy, reduced time latency, and greater detection sensitivity to maximize the operational commander's situational awareness. The SBIRS "System of Systems" architecture will consist of four satellites located in geostationary orbit, two satellites orbiting in highly elliptical orbits, and a constellation of greater than twenty satellites in low earth orbit to provide global coverage in support of SBIRS missions. The SBIRS High system of satellites is comprised of four satellites located in geostationary orbit and two satellites orbiting in highly elliptical orbits. These six satellites will perform the four infrared missions of missile warning, missile defense, technical intelligence, and battlespace characterization. Specifically, SBIRS High will provide global and theater infrared data and processed messages concerning launch, flight, and impact location of strategic and theater missiles and other infrared significant events to the National Command Authority and operational commanders. The SBIRS High component will use highly flexible tasking infrared sensor technology to combat emerging threats. Each satellite will consist of a scanning infrared sensor for global coverage and a staring sensor for accurate detection and tracking of theater-level threats. This technology will allow the SBIRS High element to detect and track shorter-range missiles in the boost phase with greater accuracy. The benefit to the warfighter will be increased accuracy in determining the missile launch point and impact point predictions in support of offensive and defensive operations. The SBIRS High ground segment architecture integrates assets from the current DSP ground segment with SBIRS unique assets to provide a highly capable, low risk system. The ground segment will consolidate three DSP operational sites and associated communications networks into a fully integrated ground segment that fuses all infrared and other data to optimize

41 performance for all infrared missions. The integrated ground segment will be implemented with modern, open systems processing and allow for modular hardware/software updates. B. SBIRS LOW OPERATIONS The SBIRS Low system of satellites will be comprised of a constellation of 25 to 30 satellites in low earth orbit. The primary function of SBIRS Low is to provide precise mid-course tracking and discrimination of objects for the SBIRS missile defense mission in theater conflicts and attacks against North America. In addition, with its low altitude putting it physically closer to the battlefield and thus allowing for higher resolution, the SBIRS Low system is well suited to support the other three SBIRS missions of missile warning, technical intelligence, and battlespace characterization. A two-stage process characterizes the SBIRS Low sensor suite concept of operations. In the first stage, the acquisition sensor scans for very bright targets in their boost phase utilizing a fast scan, large field of view, small aperture focal plane. Then, the track sensor will stare at very dim post-boost phase targets using a technique of slew and stare with a small field of view, modest aperture focal plane. Conceptually, the track sensor's field of view is similar to looking through a soda straw. An example of the entire sensor system operation is the acquisition sensor detects the infrared signature of a booster rocket, then the acquisition sensor performs a handoff to the track sensor, which maintains a ballistic track on all post-boost vehicles. Post-boost vehicles may include the reentry vehicle (warhead), an attitude control module, spent booster rocket, and decoys. As necessary, the track sensor in one satellite will "handover" a track to another track sensor in a different satellite. This tracking information is also relayed to a ground station where the decision on target engagement procedures is made based upon the current battlespace characterization. The interceptor batteries will receive cueing data from the SBIRS Low system. The goal is to launch as few interceptors as necessary to achieve the desired probability of kill. The interceptor battery's salvo doctrine, e.g., shoot-look-shoot, shoot-shoot-look, shoot four times, is determined by the operational commander based upon their current tactical assessment. Because both satellites and a missile move relative to each other, different satellites will track a target based on the time of launch, location of the launch, operability of a satellite, and track revisit scheme. Communications between satellites, between a satellite and the global